Wireless telecommunications system utilizing CDMA radio frequency signal modulation in conjuction with the GSM A-interface telecommunications network protocol

ABSTRACT

A method and apparatus for operating a wireless telecommunication system utilizing code division multiple access (CDMA) over-the-air with a Global System for Mobile communications (GSM) A-interface based network is described. A CDMA radio frequency (RF) signal interface provides a bi-directional interface to a subscriber unit, and a Global System for Mobile (GSM) communications A-interface SS7 transport provides a bi-directional interface with GSM mobile services switching center (MSC). Additionally, a transparent message transport is provided over which signaling messages defined in the GSM A-interface protocol are exchanged between the GSM MSC and a subscriber unit. Other signaling message generating by the GSM MSC and subscriber unit are processed and various actions are taken in response, including the configuration and control of signal processing resources. This configuration and control includes the allocation of vocoding and devocoding resources in accordance with the requested type of service, and the invocation of CDMA based encryption capabilities. Other actions include the allocation of CDMA traffic channel processing resources and selection resources at the start of a signaling exchange between the subscriber unit and the BSS or MSC. These resources process both voice and data calls, and signaling messages, such as registrations, from the subscriber unit. The CDMA traffic channel resources are used to perform the IS-95 style CDMA signal processing functions including modulation and demodulation.

This is a Divisional of application Ser. No. 08/575,413, filed Dec. 20,1995 now U.S. Pat. No. 5,878,036.

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates to wireless telecommunications. Moreparticularly, the present invention relates to a novel and improvedmethod and apparatus for providing wireless telecommunication serviceusing a Code Division Multiple Access (CDMA) “over-the-air” interface inconjunction with a Global System for Mobile communications (GSM)A-interface protocol interface.

II. Description of the Related Art

The Global System for Mobile communications (GSM) wirelesstelecommunications standard is a set of widely available digitaltelecommunications protocols for use within a digital wireless telephonesystem. The CSM specifications were developed by an international effortand have been adopted by the European Telecommunications StandardsInstitute (ETSI, 06921 Sophia Antipolis Cedex, France). A wirelesstelephone system configured in a manner consistent with the use of theGSM standards is shown in FIG. 1. GSM mobile-services switching center(MSC) 16 switches or connects telephone calls between the wirelesssystem access network, namely the base station subsystems (BSS) 15, andwireline based public switched telephone network (PSTN) 18, which mayalso be a public land mobile network (PLMN). GSM MSC 16 providestelephone switching, billing, subscriber unit tracking, subscriber unitauthorization, and some handoff control functionality. BSS 15 iscomprised of base station controller (BSC) 14 and any base transceiverstation(s) (BTS) 12 coupled thereto. As defined in the GSMspecifications, the interface between GSM MSC 16 and BSS 15 is referredto as the GSM “A interface,” which separates the GSM network switchingequipment from the time division multiple access (TDMA) based radioequipment. BSC 14 is involved with handoff processing and signalprocessing resource allocation within BTSs 12 so that multiplesubscriber units 10 can conduct telephone calls simultaneously. BTS 12interfaces the subscriber units 10 via radio frequency (RF) signals anda well defined “over-the-air” protocol to the GSM wireless network. BTS12 comprises radio transmission and reception devices, up to andincluding antenna devices, and also all the signal processing specificto the radio interface. BTSs can be considered as complex radio modems.Subscriber unit 10 provides generic radio and processing functions toaccess the GSM network through the radio interface to either the user ofsubscriber unit 10 or some other terminal equipment, such as a facsimilemachine or personal computer. A particular subscriber unit 10 may switchthe BTS 12 with which it interfaces as its location changes, but canonly communicate with one BTS at a given instant. Within thisapplication, the capability to switch from one BTS 10 to another BTS 10,where only one radio interface exists at any instance, is referred to assubscriber unit hard handoff.

To make a wireless telephone call, a network connection must beestablished between subscriber unit 10, often referred to as a “mobileunit,” and PSTN 18. PSTN 18 is the conventional wireline telephonesystem. To conduct the telephone call in a mobile fashion, a portion ofthe network connection is formed via the exchange of radio frequency(RF) signals between subscriber unit 10 and BTS 12. The remainingportion of the network connection is typically formed through wire basedconnections that pass through BSS 15 and through GSM MSC 16. Inaccordance with the GSM “over-the-air” protocol, which is one of theprotocols that make up the GSM wireless telecommunications standard,TDMA technology is used to establish a set of channels within the aboveidentified RF signals used to interface a subscriber unit 10 with a BTS12. These channels are used to separate and distinguish the various setsof data associated with the various telephone calls being made at anygiven time. The various sets of data include user data which normallytakes the form of digitized audio information, and signaling data whichis comprised of the signaling messages used to orchestrate theprocessing of a telephone call.

At the time of the inception of the GSM standard, the use of TDMA withinthe GSM over-the-air protocol increased the efficiency with which thegiven radio frequency bandwidth could be used to conduct wirelesstelephone calls. Increasing the efficiency with which the availableradio frequency bandwidth is used is desirable because only a limitedamount of RF bandwidth exists, and the amount of bandwidth is usuallythe limiting factor as to the number of calls that can be conducted by aparticular wireless cellular telephone system. Since the inception ofthe GSM wireless telecommunications protocol, however, other wirelesstechnologies have been perfected that allow a greater number oftelephone calls to be conducted in a given RF bandwidth. Since efficientuse of radio frequency bandwidth is highly desirable, the use of thesemore efficient technologies is now preferred.

One prominent and widely accepted example of a more efficient wirelesstelecommunications technology is Code Division Multiple Access (CDMA)signal processing and the associated over-the-air IS95 protocol adoptedby the Telecommunications International Association (TIA, 2001Pennsylvania Avenue, N.W., Washington, D.C. 20006). With CDMAmodulations techniques, each user traffic channel consists of a carriermodulated by a different high speed binary sequence, thereby spreadingthe spectrum of the waveform. Sets of user traffic channels share thesame wideband frequency spectrum allocation, and both user data andsignaling messages are transmitted over a user traffic channel.Additionally, each CDMA based BTS transmits overhead control signalingchannels that carry information to enable the subscriber unit to acquireand access the system. These overhead control channels are alsomodulated with a high speed binary sequence and combined with the usertraffic channels to comprise one wideband RF signal. Each CDMA based BTStransmits the combined RF signal, referred to as the forward CDMAchannel, and receives the combined RF outputs of a set of CDMA basedsubscriber units located within an associated coverage area, where thesecombined set of outputs are referred to as the reverse CDMA channel. Theforward CDMA channel is the sum of the forward pilot channel, theforward synchronization channel, one or more forward paging channels,and many forward user traffic channels that are each modulated with adistinct channel code and are combined with a PN spreading sequence. Thereverse CDMA channel is the sum of one or more reverse access channelsand many reverse user traffic channels that are each modulated with aunique channel code and are transmitted with a specific PN spreadingsequence.

CDMA based wireless communication systems also offer an improved methodof handoff for subscriber unit mobility. A handoff procedure known as“soft handoff” is afforded by the ability to utilize a subscriber unit'sRF signals at more than one CDMA based BTS. This “soft handoff” abilityof subscriber unit 10 to simultaneously engage in multiple RF interfaceswith multiple CDMA based BTSs 12 provides transmission path redundancyas subscriber unit 10 moves from one location to another, therebydecreasing the chances of a call being dropped and of voice samplesbeing lost. Additionally, the IS95 protocol provides higher qualitytelecommunication service when compared to GSM since the CDMA signal isless susceptible to fade and noise interference. A subscriber unitcommunicating in accordance with the IS-95 protocol also consumes lesspower than a subscriber unit communicating in accordance with the GSMover-the-air protocol because the use of extensive power controlalgorithms are included in the normal operation of a CDMA system. Thisreduced power consumption allows the life of a battery used to power anIS-95 compliant subscriber unit to be extended beyond that of a GSMcompliant subscriber unit.

Many regions having already existing GSM cellular telephone systems arereluctant to provide CDMA cellular telephone service despite it manybenefits, however. This is because the incremental performanceimprovement provided by a CDMA system may not be sufficient to justifythe cost of providing a completely new CDMA cellular telephone systemwhen a previously existing system is available. This situation is incontrast to a region in which an entirely new cellular telephone systemis to be built, where a CDMA cellular telephone system is often lesscostly to implement and provides higher quality service than a GSMcellular telephone system. If a method and system for implementing aCDMA cellular telephone system that utilized some of the existing GSMcellular telephone system infrastructure were devised, however, the costof providing CDMA cellular telephone service in a region with anoperating GSM cellular telephone system would be reduced. If thereduction were sufficient, the incremental performance benefit providedby a CDMA cellular telephone system could be justified in a greaternumber of locations. This would allow subscribers of cellular telephoneservice located in those regions to also have the benefit of CDMAcellular telephone service, and therefore such a method and system forimplementing a cellular telephone system would be highly desirable.

SUMMARY OF THE INVENTION

A method and apparatus for operating a wireless telecommunication systemutilizing CDMA over-the-air with a GSM A-interface based network isdescribed. By utilizing the GSM A-interface standard, which is definedin the GSM specifications as the interface between the GSM MSC and theBSS, the CDMA wireless telecommunications system can be implementedusing a GSM MSC conforming to the GSM specifications. This allows CDMAwireless cellular telephone service to be provided using some of theexisting operating GSM network infrastructure. In the preferredembodiment of the invention, the CDMA based BSC communicates to the GSMMSC via the A interface as it is specified in the existing GSMstandards. However, other embodiments of the invention may usemodifications to the defined GSM A interface to enhance system operationand functionality. In accordance with one embodiment of the invention,the BSS and subscriber units interface via the use of radio frequencysignals physically modulated in accordance with CDMA techniques. In thepreferred embodiment of the invention, the CDMA modulation techniquesare substantially similar to those incorporated in the IS95 wirelesstelecommunications protocol previously referenced.

A high level diagram of the functional elements used to interface asubscriber unit and a GSM MSC, in accordance with one embodiment of theinvention, is illustrated in FIG. 2. During operation of the system,CDMA RF interface 40 provides a bi-directional interface to subscriberunit 50, and GSM A-interface SS7 transport 42 provides a bi-directionalinterface with GSM MSC 52. Establishing the CDMA over-the-air interfaceand use of transparent signaling transport 44 allows the signalingmessages defined in the GSM A-interface protocol to be exchanged betweenGSM MSC 52 and subscriber unit 50. Processing and service conversion 46receives and examines certain signaling messages from CDMA RF interface40 and GSM A-interface SS7 transport 42 and takes various actions inresponse, including the configuration and control of signal processingresources 48. This configuration and control includes the allocation ofvocoding and devocoding resources in accordance with the requested typeof service, and the invocation of CDMA based encryption capabilities.Other actions include the allocation of CDMA traffic channel processingresources and selection resources at the start of a signaling exchangebetween the subscriber unit and the BSS or MSC. These resources areallocated for both the processing of voice and data calls, and forsignaling exchanges, such as registrations, between subscriber unit 50and the system. The CDMA traffic channel resources are used to performthe IS-95 style CDMA modulation and demodulation functions.

A set of call processing procedures are provided for performing varioustasks associated with the proper processing of a wireless telephone callor communication. These procedures include call initiation, callrelease, subscriber unit registration, over-the-air signal encryption,subscriber unit authentication, and the sequences of signaling messagesand processing steps associated with these procedures which aredescribed in the detailed description of the invention. In accordancewith one of the described embodiments of the invention, call initiationand subscriber unit registration are performed by first establishing aCDMA over-the-air interface between a subscriber unit and a CDMA basedBSS, and by then establishing a telecommunications network connectionbetween the subscriber unit and a GSM MSC. The invention also employsthe use of CDMA encryption techniques. CDMA encryption techniques, usedto provide subscriber information and location privacy, are initiatedand terminated via the GSM encryption procedures controlled by GSM MSC52.

In one embodiment of the invention, transparent signaling transport 44transparently passes signaling information between GSM MSC 52 andsubscriber unit 50. Transparent transport is defined as the exchange ofsignaling information between GSM MSC 52 and subscriber unit 50 suchthat no intermediate processing entity examines, modifies, or makes useof the information being transparently transported. The use of thistransparent transport mechanism allows key portions of the applicationlayer information exchanged between the CDMA based BTS and thesubscriber unit to be identical to the information exchanged between aGSM TDMA based BTS and its associated GSM subscriber unit. In thepreferred embodiment of the invention, transparent signaling transport44 passes messages defined in the GSM specifications as Direct TransferApplication Part (DTAP) messages between GSM MSC 52 and subscriber unit50. DTAP messages allow GSM MSC 52 and subscriber unit 50 to exchangedata as necessary to properly process a GSM based telephone call. TheDTAP message classification encompasses call management and subscriberunit mobility management functions. Allowing call management andsubscriber unit mobility management messages to be transparentlytransported between the GSM MSC and the subscriber unit allows theinvention to utilize many of the existing GSM call establishment relatedprocedures. This, in turn, allows the invention to utilize the existingGSM A interface definition, enabling GSM wireless communication systemoperators to reuse their existing operating GSM infrastructure equipmentin fielding a wireless communication system that utilizes CDMAover-the-air with their GSM A-interface based network.

In accordance with the present invention, a subscriber unit acquires thesystem, records system related information it receives from the BTS onthe forward CDMA overhead channels, and then is configured to receive,process and transmit signaling messages used for establishing both thebi-directional CDMA over-the-air interface and the telecommunicationsnetwork connection. A subscriber unit receives and appropriatelyprocesses CDMA radio resource, GSM call management, and GSM mobilitymanagement signaling messages. The GSM call management and GSM mobilitymanagement comprise the DTAP portion of the GSM A-interface. CDMA radioresource procedures include, but are not limited to, performing suchactions as handoff, system access attempts, and bi-directional RF signaltraffic channel establishment. GSM call management procedures include,but are not limited to, performing such actions as call establishment,supplementary service invocations, and subscriber unit alerting. GSMmobility management procedures include, but are not limited to,performing such actions as subscriber unit authentication, locationupdating, and international mobile station identity attach and detachprocedures.

BRIEF DESCRIPTION OF THE DRAWINGS

The features, objects, and advantages of the present invention willbecome more apparent from the detailed description set forth below whentaken in conjunction with the drawings in which like referencecharacters identify correspondingly throughout and wherein:

FIG. 1 is a block diagram of a cellular telephone system configured inaccordance with the GSM standards;

FIG. 2 is a functional block diagram of the message processing andservice conversion architecture used to interface a subscriber unit anda GSM MSC in accordance with one embodiment of the invention;

FIG. 3 is a block diagram of a cellular telephone system configured inaccordance with one embodiment of the invention;

FIG. 4 is a diagram illustrating the various GSM A interface messageformats transported utilizing the Signaling System Number 7 interface;

FIG. 5 is a block diagram of a base station subsystem configured inaccordance with one embodiment of the invention;

FIG. 6 is a message sequence diagram illustrating the signaling messagestransmitted during a subscriber unit terminated call initiationperformed in accordance with one embodiment of the invention;

FIG. 7 is a message sequence diagram illustrating the signaling messagestransmitted during a subscriber unit originated call initiationperformed in accordance with one embodiment of the invention;

FIG. 8 is a message sequence diagram illustrating the signaling messagestransmitted during a subscriber unit originated call release performedin accordance with one embodiment of the invention;

FIG. 9 is a message sequence diagram illustrating the signaling messagestransmitted during a network initiated call release performed inaccordance with one embodiment of the invention;

FIGS. 10A and B are a message sequence diagram illustrating thesignaling messages transmitted during a subscriber unit registrationperformed in accordance with one embodiment of the invention;

FIG. 11 is a block diagram of BSC A-interface configured in accordancewith one embodiment of the invention; and

FIG. 12 is a block diagram of a subscriber unit configured in accordancewith one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A method and apparatus for providing wireless telecommunication serviceusing a code division multiple access (CDMA) based over-the-airinterface in conjunction with a global system for mobile communications(GSM) A-interface protocol network interface is described. In thefollowing description, the invention is set forth in the context of aradio frequency signal interface operating in accordance with physicalsignal modulation technique of the IS-95 CDMA over-the-air protocol.While the described invention is especially suited for use with suchsignal modulation techniques, the use of other code division multipleaccess wireless telecommunications protocols is consistent with thepractice of the present invention. Also, while the preferred embodimentof the invention incorporates the use of the GSM A-interface, otherA-interfaces may also be employed where the use of a transparenttransport mechanism between a mobile switching center and a subscriberunit is required. The invention may also be implemented in the contextof a satellite based telecommunications system, or a point to pointwireless telecommunications system. In particular, the invention isuseful in the context of satellite based wireless telecommunicationsystem incorporating the use of “bent pipe” transmission methods thatmust interface with a telecommunications network gateway, because manygateways will utilize the GSM A-interface protocol. Furthermore, itshould be understood that the present invention is intended for use withvarious types of communications, including both voice basedcommunications as well as communications during which digital datarepresenting information other than voice is transmitted.

Throughout the application the use and transmission of various types ofinformation is described including messages, requests, orders,instructions and commands. It should be understood that this informationis constituted by electronic representations of these messages,requests, orders, instructions and commands, that are generated via theuse of electric currents, voltage potentials, electromagnetic energy, ora combination thereof. Additionally, the following description containsreference to various systems for manipulation and generation of suchinformation. In the preferred embodiment of the invention, such systemsare implemented via the use of digital and analog integratedsemiconductor circuits coupled to one another via various conductiveconnections or via the use of electromagnetic signals, or both. In otherinstances throughout the application, various well known systems aredescribed in block form. This is done to avoid unnecessarily obscuringthe disclosure of the present invention.

For purposes of the present invention, the GSM A interface definitionencompasses the user data transmission and the control signaling betweenthe GSM MSC and any connected BSCs. The control signaling is comprisedof the physical signaling transport layers and the telephone callapplication information being transported. In the GSM standard, thesignaling transport layers of the A interface are specified as themessage transfer part (MTP) and signaling connection control part (SCCP)of signaling system number 7 (SS7), as defined by the InternationalTelecommunications Union (ITU), which is well known in the art. Thetelephone call application data is transported between the GSM MSC andthe BSC within the data field of the various SCCP messages.

FIG. 3 is a block diagram of a wireless telephone system configuredduring normal operation in accordance with one embodiment of theinvention. Base transceiver stations (BTS) 102(A)-(C) are coupled to BSC104(A) and BTSs 102(D)-(F) are coupled to BSC 104(B). BSCs 104(A) and(B) are in turn coupled to GSM MSC 106 which is coupled to publicswitched telephone network (PSTN) 108 (can also be PLMN). Subscriberunit 100(A) is conducting a telephone call or other communication viathe use of radio frequency (RF) signals exchanged with BTS 102(D).Subscriber unit 100(B) is conducting a telephone call or othercommunication via the use of RF signals exchanged with both BTS 102(B)and BTS 102(C). When engaged in an RF signal interface with two or moreBTSs 102, as is the case with subscriber unit 100(B), subscriber unit100(B) is said to be in “soft handoff.” RF signals transmitted from BTS102 to subscriber unit 100 are referred to as forward link channels, andRF signals transmitted from a subscriber unit 100 to a BTS 102 arereferred to as reverse link channels. BSS 105 is made up of a BSC 104and the set of one or more BTSs 102 to which it is coupled.

In the preferred embodiment of the invention, the physical signalprocessing of both the forward and reverse link channels is performed inaccordance with the CDMA signal processing techniques of the IS-95protocol. This physical signal processing includes the use of forwardand reverse link spreading codes and channel codes during both thetransmission and reception of the forward and reverse link signals. Thechannel codes are used to establish a set of channels over which varioussets of data may be transmitted by direct sequence modulation. For theforward link, the channel codes are comprised of a set of sixty fourorthogonal binary codes referred to as Walsh codes, and for the reverselink the channel codes are comprised of a set of binary long codes thatcalculated for each subscriber unit as a function of a unique subscriberunit identification code. The spreading codes are used to diversify therange of frequencies of which the data is transmitted so as to improvethe likelihood of successful transmission. This diversification isreferred to as spreading and is also performed via direct sequencemodulation of the data being transmitted with the spreading codes. Inthe preferred embodiment of the invention, the channelization isperformed via bi-phase shift key (BPSK) modulation and the spreading isperformed via quad-phase shift key modulation (QPSK), in a similarfashion to an IS95 compliant system.

In one embodiment of the invention, the forward link channels includeone or more pilot channels, synchronization channels, paging channels,and user traffic channels, each defined by modulation with apredetermined forward link channel code. The reverse link channelsinclude one or more access channels and many user traffic channels eachdefined by modulation with a unique reverse link long code. In order forthe transmission and reception of the forward and reverse link signalsto be performed properly, the state of the channel and spreading codesused to process the forward and reverse link signals during receptionand transmission must be synchronized. This synchronization is achievedduring call set-up and is referred to as signal acquisition, manyprocesses for which is well known in the art. Data being transmitted viaeither the forward or reverse link is divided into frames that alsocontain error correction bits and frame header bits. The frame headerbits indicate whether the data contained in the frame is signaling dataor traffic data, or a combination thereof. Traffic data is the databeing transmitted by the user when the call is in progress and isusually digitized voice or audio information, but can be any type ofuser data. To transmit a complete signaling message, it is generallynecessary to transmit multiple frames of signaling data, which areassembled into the signaling messages by the receiving system. As notedabove, signaling messages are used to exchange any information betweenthe various systems shown in FIG. 3 necessary to setup and process atelephone call. Once assembled each signaling message contains messageheader bits which indicate the type of signaling message.

Still referring to FIG. 3, as noted above, GSM MSC 106 providestelephone switching, billing, and subscriber unit tracking andauthorization functionality. GSM MSC 106 and BSC 104 communicate inaccordance with the GSM A-interface protocol which is part of the GSMstandard. In order to set up a telephone call connection using GSM MSC106, a particular set of signaling messages must be generated in aparticular order containing a particular set of information. That is,BSC 104 must generate and transmit the proper set of signaling to GSMMSC in the proper order depending on the required network connectionsand the signaling messages received from GSM MSC 106. The order,information, and format associated with these sets of signaling messagesare defined by the GSM A-interface protocol. As might be expected, theorder, information and format differ substantially from any interfaceassociated with a comparable MSC operating within a CDMA cellulartelephone system. In a similar fashion, a subscriber unit 100 operatingin accordance with the IS-95 or other CDMA based protocol must exchangea predetermined set of messages with BTS 102 in a predetermined orderand in a predetermined format to properly set up and process a telephonecall. As also might be expected, the CDMA over-the-air interface differssubstantially with the over-the-air interface associated with GSMwireless telecommunications systems.

The signaling messages associated with the GSM A-interface protocol areseparated into two categories: Direct Transfer Application Part (DTAP)messages and BSS Management Application Part (BSSMAP) messages. DTAPcontain data relevant to the operation of subscriber unit 100 and MSC106, and therefore do not directly affect the operation of BSS 105.BSSMAP messages are generally associated with the operation of BSS 105and may cause resource allocation or provide information necessary tothe proper operation of BSS 105. A BSSMAP message may affect the entireoperation of BSS 105, or just the operation of a single phone call. Alsoin accordance with the GSM A interface, the signaling messages aretransmitted via a Signaling System Number 7 (SS7) signaling link and theassociated message transfer part (MTP) and signaling connection controlpart (SCCP). MTP utilizes three message formats to transmit binary datavia a serial link. The three message formats are referred to as messagesignal units (MSU), link status signal units (LSSU), and fill-in signalunits (FISU). The fields associated with each message format areillustrated in FIG. 4 with the number of bits associated with each fieldindicated below. The messages are separated via the use of a flag byte(FL) which contains a logic zero followed by a series of six logic onesfollowed by a logic zero (01111110). Within the messages defined by theflag bytes, a logic zero is inserted in any series of more than fivelogic ones.

Each message format is comprised of a header section containing abackward sequence number (BSN), a backward indication bit (BIB), aforward sequence number (FSN), a forward indication bit (FIB), and alength indicator (LI) followed by two buffer bits. Additionally, eachmessage format includes a set of check bits (CK) inserted just beforethe terminating flag byte. For FISUs, no additional data fields areincluded. For LSSUs, a one or two byte status field (SF) is includedwhich indicates one of six different status indications dealing withalignment status and out of service. For MSUs, a signal byte serviceinformation octet (SIO) and a two or more byte signal information field(SIF) are included. Since each message format contains a differentamount of information, the type of message is determined from the lengthindicator field (LI). The signaling messages transmitted in accordancewith the GSM A-interface are sent via a MSU with the data associatedwith the GSM A-interface signaling message placed in the SIF. Moreparticularly, messages transmitted in accordance with the GSMA-interface are placed in SCCP messages which include a routing label(RL), an SCCP message type code, an SCCP header, and an SCCP data fieldas shown. The SCCP message type code is typically considered as asubfield of the SCCP header. The SCCP message is terminated with an endof optional parameters flag (EOP). If the BSSMAP message transportedinside the SCCP message is the type which relates to a single phonecall, the phone call with which the message is associated is indicatedin the connection identifier field in the SCCP header (not shown). ABSSMAP or DTAP message is contained within the SCCP data parameter withthe type of message indicated by the discrimination bit (DIS) located atthe beginning of the SCCP data field. If a BSSMAP message is beingtransmitted, the length is indicated in the length (LEN) field.Following the length are the type of BSSMAP message and the rest of themessage. If a DTAP message is being transmitted, the length is indicatedin the length (LEN) field, and the sub category of the DTAP message isindicated in the protocol discrimination field. Any additional dataassociated with the particular DTAP message including the message typeis placed in the message data field.

FIG. 5 is a block diagram of BSS 105 configured to provide CDMAover-the-air telecommunications service in conjunction with a GSMA-interface protocol network interface in accordance with one embodimentof the invention. BTSs 102 are coupled to BSC 104 via wirebased links,which in the preferred embodiment of the invention constitutes a T1 orE1 connection, although other connections may be substituted includingthe use of microwave link. Within BSC 104, CDMA interconnect subsystem200 is coupled to the set of BTSs 102 shown. CDMA interconnect subsystem200 is also coupled to call control processor 202, selection subsystem204, and BSC A-interface 206. CDMA interconnect subsystem 200 serves asa message and traffic router between the connected coupled entities andin the preferred embodiment of the invention is comprised of anasynchronous fixed length packet transport system. Data processing andservice options system 210 is coupled to selection subsystem 204 andexchanges traffic data with switch 212. Switch 212 provides an interfaceto GSM MSC 106 of FIG. 2, consisting of traffic data and signaling, andalso exchanges control data with call control processor 202. In thepreferred embodiment of the invention, this signaling data istransmitted using the ITU Signaling System Number 7 (SS7) protocol asspecified in the GSM A-interface protocol, the use of which is wellknown in the art. Each of the connections shown within BSC 104 is a highspeed digital connection such as fast Ethernet, the use of which is alsowell known in the art. In alternative embodiments of the invention,switch 212 may be replaced with a simpler cross connect device, causingBSC A-interface 206 to be coupled directly to GSM MSC 106. However, theuse of switch 212 is preferred because it allows BSC 104 to be coupledto multiple MSC systems if necessary, each of which can providealternative types of network service including IS41 service, the use ofwhich is well known in the art. If BSC 104 is coupled to multiple MSCsystems, additional BSC interface systems similar to BSC A-interface 206are utilized in the preferred embodiment of the invention, not all ofwhich must incorporate the use of the GSM A-interface protocol.

In the preferred embodiment of the invention, the systems that make upBSS 105 communicate and exchange traffic and signaling data via the useof an internal BSS protocol in which fixed length data packets areexchanged among the various other systems via CDMA interconnectsubsystem 200, or via direct routing between the two systems involved.CDMA interconnect subsystem 200 performs this routing via the use of anaddress contained in each fixed length data packet Generally, a firstsystem transmitting a data packet to a second system places the addressof that second system in the data packet, and then provides that datapacket to CDMA interconnect subsystem 200. In the case of some adjacentsystems, such as selection subsystem 204 and data processing and serviceoption system 210, data packets are passed directly. Whether aparticular fixed length packet contains traffic data or signaling datais indicated by a packet header bits contained in each packet. Datapackets containing traffic data are referred to as traffic packets anddata packets containing signaling data are referred to as signalingpackets. Control information is also exchanged between some systemswithin BSS 105 via the use of dedicated connections such as the oneshown between call control processor 202 and switch 212. Other methodsof networking the various systems within BSS 105 shown in FIG. 5, otherthan via CDMA interconnect subsystem 200, are consistent with theoperation of the present invention.

A signaling message constitutes a complete instruction used to controlboth the operation of the various systems that make up BSS, as well asto exchange information with subscriber unit 100 or GSM MSC 106. Acomplete signaling message is transmitted via one or more signalingpackets that are assembled by the receiving system to generate thesignaling message being transmitted. In accordance with one embodimentof the present invention, a sub category of signaling message is definedthat are transmitted through BSS 105 without affecting the operation ofBSS 105. For purposes of this application such signaling messages arereferred to as “transport messages,” and the availability of transportmessages forms a transparent transport function within BSS 105. Thetransparent transport function is generally used for exchanging aspecific category of signaling messages between GSM MSC 106 andsubscriber unit 100, defined as DTAP messages, by way of BSS 105. Duringthe operation of BSS 105, call control processor 202 and BSC A-interface206 configure and control the various other systems within BSS 105 viathe use of other signaling messages, and generally throughout theapplication any configuration or other control exercised by call controlprocessor 202 and BSC A-interface 206 is performed via the use of thesesignaling messages, which are passed as described above in the preferredembodiment of the invention, although the use of other message passingmechanisms such as direct interconnect between systems is alsoconsistent with the present invention. In the preferred embodiment ofthe invention, call control processor 202 and BSC A-interface 206 areimplemented via the use of computer systems controlled by softwareinstructions. (Not shown)

One type of configuration and control performed by BSC A-interface 206includes the allocation of selection resources within selectionsubsystem 204. A selection resource provides a bi-directional interfacebetween subscriber unit 100 and any system within BSC 104 by way of oneor more BTSs 102. The functions associated with this bi-directionalinterface include matching multiple copies of a data frame generated bytwo or more BTSs and selecting the highest quality data frame from theset of copies for further processing. This selection in made based onquality indication information placed in each frame by each BTS 102. Themultiple copies of a frame are generated when subscriber unit 100 isengaged in multiple RF interfaces with multiple BTSs 102 during a softhandoff condition. Additionally, a selection resource receives datapackets directed towards a subscriber unit 100, and forwards a copy ofthe data packet to each BTS 102 engaged in an RF interface with thatsubscriber unit 100. Each selection resource has its own internaladdress so that packets associated with the call being processed can berouted to that selection resource within selection subsystem 204. Eachselection resource also tracks the set of BTSs 102 with which thesubscriber unit 100 to which it is assigned is interfacing. In thepreferred embodiment of the invention, the selection resource isconstituted by a microprocessor or digital signal processor controlledby software instructions stored in a memory unit also located withinselection subsystem 204. (Not shown)

BSC A-interface 206 also configures data processing and service optionssystem 210 to process data from selection subsystem 204 in a variety ofways based on the services necessary to process the telephone call. Thetypes of signal processing services provided include vocoding anddevocoding the voice traffic data associated with a telephone call, themodulating and demodulation of tones and other signals used for thetransmission of fax and other digital data via a standard PSTNconnection, and the encryption of user and signaling data. In thepreferred embodiment of the invention, the signal processing is done viathe use of a digital signal processing integrated circuit located withindata processing and service options system 210 and controlled via theuse of software instructions stored in a memory system, the use of whichis well known in the art. (Not shown) Another function performed by BSCA-interface 206 is to receive DTAP signaling messages from GSM MSC 106transmitted in accordance with the A-interface, and to transport thosesignaling messages to the appropriate subscriber unit 100 by placing themessage in transport messages, and forwarding the transport messages tothe selector resource associated with the telephone call. Upon receivingthe transport messages, the selector resource will forward the transportmessage to the subscriber unit 100 via the CDMA forward user trafficchannel.

As noted above, data is exchanged between a BTS 102 and a subscriberunit 100 via multiple frames containing frame header bits indicating thetype of data contained in that frame. In the preferred embodiment of theinvention, both signaling and traffic data may be transmitted in asingle frame in accordance with the IS-95 standard. No address iscontained in the frame during the over the air transmission as thedestination and source of each frame are indicated by the channel codeused to modulate the data. In the preferred embodiment of the invention,each frame transmitted via the reverse link is received by a particularchannel processing element (not shown) within a BTS 102. Each channelprocessing element in turn knows the internal address of the selectorresource processing the call, and after extracting a frame from thereverse link signal the channel processing element forwards the frame tothe selector resource. The selector resource then assembles signalingmessages from frames containing signaling data and determines the typeof signaling message based on signaling messages header bits containedin the signaling message. Transport signaling messages are transparentlyrouted to BSC A-interface 206 by the selection resource via the use ofthe BSS transport messages described above. BSC A-interface proceeds toplace a connection identifier associated with the phone call into theSCCP header field based on the selection resource transmitting thetransport signaling message, and to transparently forward the transportsignaling messages to the GSM MSC in accordance with the A-interfaceprotocol. If the message is a non-transport or local signaling message,the selector resource and BSC A-interface 206 will process the messageinternally.

In accordance with one embodiment of the present invention, variousprocedures must be performed via the orderly exchange of signalingmessages between the various systems shown in FIG. 5 in order toproperly process a telephone call. The various procedures include callinitiation, call release, and subscriber unit registration. FIGS. 6-10are a set of a message sequence diagrams illustrating the signalingmessages exchanged during the processes of call initiation, callrelease, and subscriber unit registration in accordance with oneembodiment of the invention. The vertical lines shown in FIGS. 6-10 areeach associated with the system identified in the box at the top of eachline. The systems are subscriber unit 100, BTS 102, selector subsystem204, call control processor 202, data processing and service optionssystem 210, BSC A-interface 206, and GSM MSC 106. A horizontal arrowrunning between two vertical lines indicates the exchange of a signalingmessage between the associated systems. Time advances from top tobottom, so the higher up horizontal lines occur before those horizontallines located lower down on the page. As indicted at the bottom of eachpage, messages exchanged between subscriber unit 100 and BTS 102 aretransmitted via the bi-directional over-the-air interface, and messagesexchanged between GSM MSC 106 and BSC A-interface 206 are transmitted inaccordance with the GSM A-interface.

As noted above, a GSM signaling message exchanged between GSM MSC 106and BSC A-interface 206 is transported within an SCCP signaling messagewhich is contained within a message signaling unit (MSU) in accordancewith the SS7 standard. Upon reception of an SCCP signaling message, BSCA-interface 206 first determines whether the message is associated witha particular communication or is directed to the operation of the entireBSS by examining the SCCP message type code field. If the message isassociated with a particular communication or telephone call, BSCA-interface 206 determines which communication via the use of aconnection identifier contained in the SCCP header. BSC A-interface 206then determines if the message is a DTAP or BSSMAP message by examiningthe discrimination field of the GSM A interface signaling message. Ifthe GSM signaling message is a DTAP message, BSC A-interface proceeds totransparently transport the signaling message via a transport message asdescribed above. If the message is a BSSMAP message, BSC A-interfacedetermines the specific BSSMAP message through examination of the BSSMAPmessage type field. Based on the BSSMAP message type, BSC A-interfaceperforms various steps as described below.

It should also be noted that for the purposes of the followingdescription, signaling messages exchanged between selection subsystem204 and subscriber unit 100 are shown by a single horizontal linebetween the two systems. Actually, however, the signaling message passesby way of one or more BTSs 102. The single line is used for ease ofdrawing when the signaling message requires no control processing orresource allocation by BTS 102. Similarly, signaling messages exchangedbetween BSC A-Interface 206 and GSM MSC 106 pass through switch 212,however a single line is shown because switch 212 performs no processingthat is particularly relevant to the present invention. The CDMAover-the-air channel used to transmit a message to or from subscriberunit 100 is indicated in parentheses next to the associated message witha ‘P’ indicating a forward link paging channel, an ‘A’ indicating areverse link access channel, and a ‘T’ indicating the forward link usertraffic channel or the reverse link user traffic channel depending onthe direction of transmission. Additionally, in FIGS. 6, 7 and 10“traffic channel setup” is the process associated with establishing theforward and reverse link user traffic channel interface betweensubscriber unit 100 and BTS 102 and is indicated at the far left of thefigure. “Network setup” is the process of establishing atelecommunications network connection with the other telecommunicationssystem involved in the call and is also indicated at the far left.Signaling messages transparently routed via the use of transportmessages are indicated by the notation “xport” with the associatedsignaling message in parentheses, and are referred to as “transportmessages” throughout the specification.

In FIGS. 8 and 9, “network release initiation,” indicated on the farleft of the figures, is the process of beginning the teardown andrelease of the network resources involved in the telephone call. Also inFIGS. 8 and 9, “traffic channel interface teardown” is the process ofreleasing the resources associated with the bi-directional radiofrequency signal interface between subscriber unit 100 and BSS 105 (FIG.3). It should also be noted that the message sequence diagram shown inFIGS. 6-10 do not show every message transmitted, but only thoseparticularly relevant to the present invention. Some signaling messagesdiscussed below are also not shown for ease of drawing. Additionally,each signaling message shown that is transmitted within BSS 105 isexchanged in accordance with the internal packet based protocoldescribed above, and therefore passes through CDMA interconnectsubsystem 200 of FIG. 5 in the preferred embodiment of the invention.

FIG. 6 is a message sequence diagram of a subscriber unit terminatedcall initiation procedure performed in accordance with one embodiment ofthe invention. A subscriber unit terminated call initiation procedureresults from the initiation of a telephone call or communication by atelecommunications entity other than a subscriber unit 100 interfacingwith the wireless telecommunications system shown in FIG. 4, such as asubscriber unit of PSTN 108, a wireless subscriber unit 100 interfacingwith another wireless telecommunications systems, or even a dataterminal. The subscriber unit terminated call initiation begins when GSMMSC 106 transmits paging message 300 to BSC A-interface 206 inaccordance with the A-interface protocol. In accordance with theA-interface protocol, page message 300 indicates the subscriber beingpaged, identified by the international mobile subscriber identity, thetype of channel required on the over-the-air interface, a cellidentifier list which indicates the set of cells most recentlyassociated with the subscriber unit, and, if available, the temporarymobile subscriber identity. BSC A-interface 206 first examines thereceived page message 300 to determine if it is a BSSMAP message.

After identifying page message 300 as a BSSMAP message, BSC A-interface206 determines that page message 300 is a page message by examining theBSSMAP message type field. Upon determining that page message 300 is apage message, BSC A-interface 206 proceeds to generate a set ofsignaling messages for establishing a bi-directional CDMA modulated RFchannel between BTS 102 and the subscriber unit 100 to which pagemessage 300 is directed. In the preferred embodiment of the invention,this set of signaling messages begins with the transmission of BSS pagerequest 302, which includes the cell identifier list, to call controlprocessor 202. Call control processor 202 responds by transmitting BTSpage request 303 to a set of BTSs 102 indicated by the cell identifierlist. Each BTS 102 responds by broadcasting page message 304 to theassociated cell via the forward link paging channel. If the page isreceived by subscriber unit 100, it responds by transmitting channelrequest message 306 to a BTS 102 via the reverse link access channel.Channel request message 306 may contain information about the type ofservice requested for the call, if such information is included in pagemessage 304.

BTS 102 responds to channel request 306 by transmitting BSS channelrequest 310 to BSC A-interface 206, and by transmitting BTS acknowledgemessage 308 to subscriber unit 100 via the paging channel. Thetransmission of BTS acknowledge message 308 is optional in the preferredembodiment of the invention. BSC A-interface 206 continues to establishthe bi-directional user traffic channel interface by responding to BSSchannel request 310 with the transmission of BSS call setup request 312to call control processor 202. Call control processor 202 allocatesselector and service resources for the call and indicates the result ofthe allocation to BSC A-interface 206 in BSS call setup response 314.Upon receiving BSS call setup response 314, BSC A-interface 206transmits selector call setup request 316 to selection subsystem 204.Selection subsystem 204 initializes the selector resource assigned toprocess the call and indicates this to BSC A-interface 206 with selectorcall setup response 318. Upon receipt of selector call setup response318, BSC A-interface 206 transmits radio link setup request 319 toselection subsystem 204. Selection subsystem 204 responds bytransmitting channel resource request 320 to BTS 102.

Upon receipt of channel resource request 320, BTS 102 allocates channelprocessing resources to modulate and demodulate the forward and reverselink user traffic channels associated with the telephone call, andtransmits channel resource response message 322 to selection subsystem204. Selection subsystem 204 responds by transmitting connect request324 to BTS 102 which responds by transmitting connect response 326 toselection subsystem 204. Selection subsystem 204 then transmits nulltraffic data 328, begin traffic data message 330, and null traffic data332 to BTS 102. BTS 102 responds to begin traffic data message 330 andnull traffic data 332 by transmitting null traffic data 336 tosubscriber unit 100 via the forward link user traffic channel. Selectionsubsystem 204 also transmits radio link resource indication 334 to BSCA-interface 206. Upon receipt of radio link resource indication 334, BSCA-interface 206 transmits BTS channel assignment message 338 to BTS 102which responds by transmitting channel assignment message 340 tosubscriber unit 100 via the forward link paging channel. Subscriber unit100 uses the assigned channel information contained in channelassignment message 340 to begin processing the assigned forward linktraffic channel, and it transmits reverse link traffic channel preamble342 on the reverse link user traffic channel so that BTS 102 can acquirethe reverse link traffic channel from subscriber unit 100. Once thereverse link traffic channel has been acquired, BTS 102 transmits beginreverse link message 344 to selection subsystem 204. Selection subsystem204 responds by transmitting reverse link acknowledge 346 to subscriberunit 100 via the forward link traffic channel. Additionally, selectionsubsystem 204 transmits radio link setup response message 348 to BSCA-interface 206. Upon receipt of reverse link acknowledge 346, thebi-directional RF interface has been established.

Having established forward and reverse link traffic channel interfaceswith BTS 102, subscriber unit 100 initiates a telecommunications networkconnection establishment procedure by transmitting page response 350 toselector subsystem 204. Page response 350 causes selector subsystem 204to transmit BSS page response 352 to BSC A-interface 206. BSCA-interface 206 receives BSS page response 352, which indicatessubscriber unit 100 is prepared to establish a network connection,stores the classmark information of subscriber unit 100, and initiatesan SCCP connection by sending an SCCP connection request containingcomplete layer 3 information message 354 to GSM MSC 106 in accordancewith the A-interface protocol. Complete layer 3 information message 354contains the contents of BSS page response message 352 and is part ofthe GSM A-interface protocol and therefore well known in the art. GSMMSC 106 responds by transmitting cipher mode command 358 to BSCA-interface 206. Cipher mode command 358 contains encryption informationincluding a ciphering key, the list of possible encryption algorithms touse based on the capabilities of subscriber unit 100, and the cipherresponse mode which may request the international mobile equipmentidentity.

Upon determining that cipher mode command 358 is a BSSMAP message andthen further determining it is a cipher mode command, BSC A-interface206 selects one of the possible encryption algorithms and transmits BSScipher mode command 360 to selector subsystem 204. Selection subsystem204 initiates over-the-air encryption procedures by transmitting ciphermode command 362 to subscriber unit 100 via the forward link trafficchannel. After processing cipher mode command 362, subscriber unit 100transmits cipher mode complete message 364 via the reverse link trafficchannel to selection subsystem 204. Upon receiving cipher mode completemessage 364, selection subsystem 204 begins to performencryption-decryption on all additional signaling and call dataassociated with the telephone call by changing to a private reverse linkchannel code, or long code, substantially in accordance with the IS-95standard. It should be noted that other methods of ciphering andencryption are consistent with the operation of the present invention.Selection subsystem 204 then transmits BSS cipher mode complete message366 to BSC A-interface 206 indicating the cipher mode configurationoperation has been completed. BSC A-interface 206 responds bytransmitting cipher mode complete command 368 indicating the chosenencryption algorithm and the international mobile equipment identifier,if requested, to GSM MSC 106 in accordance with the A-interfaceprotocol.

Next, GSM MSC 106 transmits setup message 370 to BSC A-interface 206.Setup message 370 contains various types of information about thetelephone call being established including the type of service, the rateof transmission, the type of data being transmitted, and the type ofvoice encoding. The use of setup message 370 is part of the GSMA-interface protocol and therefore well known in the art. Upondetermining setup message 370 is a DTAP message, BSC A-interface 206transparently transports the message contents via transport message 372to selection subsystem 204. In the preferred embodiment of theinvention, BSC A-interface 206 does not know setup message 370 is infact setup message, but only that it is a DTAP type message as it doesnot look beyond the discriminator bits, This simplifies the processingrequired of BSC A-interface 206 and allows for transparent transport.Upon determining transport message 372 is a transport message, selectionsubsystem 204 forwards the message contents via transport message 374 tosubscriber unit 100 via the forward link traffic channel. Afterreceiving transport message 374, subscriber unit 100 passes the contentsof the message, which is the DTAP setup message, to the GSM messageprocessing portion of subscriber unit 100. That portion of subscriberunit 100 responds by transmitting call confirm to selection subsystem204 within transport message 376. A call confirm either confirms thetype of service set forth in setup message 370, or proposes analternative type of service. Selection subsystem 204 transparentlytransports the contents of transport message 376 to BSC A-interface 206via transport message 378 containing the call confirm. Continuing thetransparent transport processes, BSC A-interface 206 forwards themessage contents via DTAP call confirm message 380 to GSM MSC 106 inaccordance with the GSM A-interface protocol.

Upon receipt of call confirm message 380 GSM MSC 106 transmitsassignment request 382 to BSC A-interface 206. Assignment request 382indicates the channel type, priority, circuit identity code (networktimeslot), downlink DTX flag (variable rate transmission), interferenceband (frequency hopping) to be used, and classmark information 2 (typeof subscriber unit). The channel type is the type of data that is to betransmitted during the transmission, for example fax, voice, orsignaling. Assignment request 382, a BSSMAP message, causes BSCA-interface 206 to negotiate the type of CDMA service necessary toprocess the telephone call with subscriber unit 100. This negotiationbegins with the transmission of BSS service request 386 to selectionsubsystem 204, which responds by transmitting service request 388 tosubscriber unit 100 via the forward link traffic channel. Servicerequest 388 indicates the parameters of the radio link necessary inorder to provide the requested data service including the data rate, andsubscriber unit 100 responds by transmitting service response 389 toselector subsystem 100, which indicates whether that type of radio linkis acceptable. If service response 389 indicates the type of service isacceptable, selector subsystem 204 transmits service connect message 390to subscriber unit 100 via the forward link traffic channel, whichcauses subscriber unit 100 to transmit service connect complete message391 to selection subsystem 204 via the reverse link traffic channel.

Selector subsystem 204 then indicates the successful service negotiationto BSC A-interface 206 by transmitting BSS service response 392. Uponreceiving BSS service response 392, BSC A-interface 206 allocatesresources for processing the call in accordance with the type of servicevia the transmission of BSS resource allocation message 384 to dataprocessing and service options system 210. Data processing and serviceoptions system 210 then allocates call processing resources forprocessing any traffic data received. In an alternative embodiment ofthe invention, the service options resource allocation is performed inresponse to the channel request message 310. Additionally, BSCA-interface 206 allocates a connection within switch 212 to create atraffic channel between GSM MSC 106 and data processing and serviceoptions system 210 to carry the traffic data associated with the call.(Message to switch 212 not shown) BSC A-interface 206 then indicates theservice negotiation has been completed via transmission of assignmentcomplete message 394 to GSM MSC in accordance with the GSM A-interfaceprotocol.

Upon completion of the service negotiation, the GSM message processingportion of subscriber unit 100 indicates to GSM MSC 106 that it isalerting the user of subscriber unit 100 by transmitting an alertingmessage via transport message 400. The alerting message is transparentlytransported by selector subsystem 204 to BSC A-interface via transportmessage 398, and then to GSM MSC 106 by BSC A-interface via DTAPalerting message 396. At this point, GSM MSC 106 may generate theringback tone towards the calling party. If the call is answered bysubscriber unit 100, it indicates the answer event to GSM MSC 106 bytransmitting a connect within transport message 402 to selectionsubsystem 204 via the reverse link traffic channel. The connect istransparently transported by selector subsystem 204 to BSC A-interfacevia transport message 404, and then to GSM MSC 106 by BSC A-interfacevia DTAP connect message 408. Upon receipt of connect message 408, GSMMSC ceases the ring back if provided, and transmits connect acknowledgemessage 410 to BSC A-interface 206. BSC A-interface 206 transparentlyforwards connect acknowledge message 410 to selection subsystem 204 viatransport message 412. Selection subsystem 204 then continues thetransparent transport via the transmission of transport message 414 tosubscriber unit 100 via the forward link traffic channel. Upon receiptof transport message 414 by subscriber unit 100, a stable call state hasbeen established and the subscriber unit terminated call originationprocess is completed.

FIG. 7 is a message sequence diagram illustrating the signaling messagestransmitted during a subscriber unit originated call initiationprocedure performed in accordance with one embodiment of the invention.A wireless subscriber unit originated call initiation procedure resultsfrom a telephone call initiated by a subscriber unit 100 of FIG. 2. Thesubscriber unit originated call initiation procedure begins with channelrequest message 506 transmitted from subscriber unit 100 to BTS 102 viathe reverse link access channel. In the preferred embodiment of theinvention, channel request message 506 contains information about thetype of service being requested, however, this information may beprovided in other messages in alternative embodiments of the invention.BTS 102 responds to channel request 506 by transmitting BSS channelrequest 510 to BSC A-interface 206, and by transmitting BTS acknowledgemessage 508 to subscriber unit 100, although the transmission of BTSacknowledge message 508 is optional in the preferred embodiment of theinvention. BSC A-interface 206 responds by generating a set of signalingmessages for establishing a bi-directional CDMA modulated RF signalinterface between subscriber unit 100 and BTS 102. The process ofestablishing such a bi-directional interface begins when BSC A-interface206 transmits BSS call setup request 512 to call control processor 202.Call control processor 202 allocates selector and service resources forthe call and indicates the result of the allocation to BSC A-interface206 in BSS call setup response 514. Upon receiving BSS call setupresponse 514, BSC A-interface 206 transmits selector call setup request516 to selection subsystem 204. Selection subsystem 204 initializes theselector resource assigned and indicates this to BSC A-interface 206with selector call setup response 518. Upon receipt of call setupresponse 518, BSC A-interface 206 transmits radio link setup request 519to selection subsystem 204. Selection subsystem 204 responds bytransmitting channel resource request 520 to BTS 102.

Upon receipt of channel resource request 520, BTS 102 allocates channelprocessing resources to modulate and demodulate the forward and reverselink user traffic channels associated with the telephone call, andtransmits channel resource response message 522 to selection subsystem204. Selection subsystem 204 responds by allocating a selection resourcefor processing the call, and by transmitting connect request 524 to BTS102, which responds by transmitting connect response 526 to selectionsubsystem 204. Selection subsystem 204 then transmits null traffic data528, traffic data message 530, and null traffic data 532 to BTS 102. BTS102 responds to begin traffic data message 530 and null traffic data 532by transmitting null traffic data 536 to subscriber unit 100 via theforward link traffic channel. Selection subsystem 204 also transmitsradio link resource message 534 to BSC A-interface 206. Upon receipt ofradio link resource message 530, BSC A-interface 206 transmits BTSchannel assignment message 538 to BTS 102 which responds by transmittingchannel assignment message 540 to subscriber unit 100 via the forwardlink paging channel

Subscriber unit 100 uses the assigned channel information contained inchannel assignment message 540 to begin processing the data received viathe assigned forward link traffic channel. It also transmits reverselink traffic channel preamble 542 so BTS 102 can acquire the reverselink traffic channel from subscriber unit 100. Once the reverse linksignal has been acquired, BTS 102 transmits begin reverse link message544 to selection subsystem 204. Selection subsystem 204 responds bytransmitting reverse link acknowledge 546 to subscriber unit 100 via theforward link traffic channel. Additionally, selection subsystem 204transmits radio link resource message 548 to BSC A-interface 206. Atthis point, the bi-directional link has been established and networkconnection setup begins.

Upon receipt of reverse link acknowledge message 546, subscriber unit100 initiates network connection setup by transmitting call managementservice request 550 to selection subsystem 204 via the reverse linktraffic channel. Selection subsystem 204 responds by transmitting BSScall management service request 551 to BSC A-interface 206. BSCA-interface 206 stores the classmark information contained in themessage, generates complete layer three information message 552containing the information sent in BSS call management service request551, and initiates an SCCP connection by sending complete layer threeinformation message 552 inside an SCCP connection request message to GSMMSC 106 in accordance with the A-interface protocol. Complete layerthree information message 552 is part of the GSM A-interface protocoland therefore well known in the art.

GSM MSC 106 responds by transmitting authentication request 553 to BSCA-interface 206. BSC A-interface 206 identifies message 553 as a DTAPmessage, and it transparently forwards the contents of the message toselection subsystem 204 via transport message 554. Selection subsystem204 determines transport message 554 is of a transport message type andtransparently forwards the contents of the message to subscriber unit100 by transmitting transport message 555 via the forward link trafficchannel. Subscriber unit 100 receives transport message 555 andtransports the contents to an internal GSM message processing portionwhich responds by transmitting transport message 556 containing anauthentication response to selector subsystem 204 via the reverse linktraffic channel. Upon determining the transport message 556 is atransport message, selection subsystem 204 transparently forwards thecontents of the message to BSC A-interface 206 via transport message557. BSC A-interface 206 continues the transparent transport byforwarding DTAP authentication response 558 to GSM MSC 106 in accordancewith the GSM A-interface protocol.

GSM MSC 106 responds by transmitting cipher mode command 559 to BSCA-interface 206. Upon determining that message 559 is a BSSMAP messageand then further determining it is a cipher mode command, BSCA-interface 206 begins over-the-air encryption initiation procedures bytransmitting BSS cipher mode command 560 to selection subsystem 204.Upon receiving BSS cipher mode command 560, selection subsystem 204transmits cipher mode command 562 to subscriber unit 100 via the forwardlink traffic channel. After processing cipher mode command 562,subscriber unit 100 transmits cipher mode complete message 564 via thereverse link traffic channel to selection subsystem 204 and begins toencrypt all subsequent transmissions. Upon receipt of cipher modecomplete message 564, selector subsystem 204 begins to performencryption-decryption on all additional signaling and call dataassociated with the telephone call. In the preferred embodiment of theinvention, this encryption is performed via the use of private channelcodes in accordance with the IS-95 specification; however, the use ofalternative encryption methods is consistent with the operation of thepresent invention. Selection subsystem 204 then transmits BSS ciphermode complete message 566 to BSC A-interface 206. BSC A-interface 206responds by transmitting cipher mode complete command 568 to GSM MSC 106in accordance with the GSM A-interface protocol indicating theconfiguration for encryption is complete.

Having a secure bi-directional channel established, subscriber unit 100transmits setup information to GSM MSC 106 by transmitting setup message570 to selection subsystem 204. Setup message 570 contains various typesof information about the telephone call being established including thedialed digits, type of service, the rate of transmission, the type ofdata being transmitted, and the type of voice encoding. Selectionsubsystem 204 transparently forwards the setup message via transportmessage 572 to BSC A-interface 206. BSC A-interface 206 continues thetransparent transport of the setup message by transmitting transportmessage 574 to GSM MSC 106 in accordance with the GSM A-interfaceprotocol. After receiving transport message 572 and initiating theconnection to the called party, GSM MSC 106 transmits transport message576 containing a call proceeding message to BSC A-interface 206. A Callproceeding messages indicates that the network connection is beingestablished, and that no more call establishment information will beaccepted. BSC A-interface 206 responds by transparently transmitting thecall proceeding message within transport message 578 to selectionsubsystem 204. Selection subsystem 204 responds by transmittingtransport message 580 containing the call proceeding message tosubscriber unit 100 via the forward link traffic channel.

After transmitting call proceeding message 576, GSM MSC 106 alsotransmits assignment request 582 to BSC A-interface 206. In response,BSC A-interface 206 continues to configure the BSS for processing thecall by transmitting BSS assignment request 586 to selection subsystem204, which responds by transmitting service connect 589 to subscriberunit. 100 via the forward link traffic channel. In response, subscriberunit 100 transmits service connect complete message 591 to selectionsubsystem 204 via the reverse link traffic channel indicating the typeof service is acceptable. (Note, the use of a both a service requestmessage and a service response message as shown in FIG. 4 is omittedhere because it is highly likely that the service will be acceptable tosubscriber unit 100 because subscriber unit 100 made the initial servicerequest when initiating the telephone call.) Selection subsystem 204proceeds to transmit BSS service response 592 to BSC A-interface 206 andBSC A-interface 206 responds by transmitting assignment complete message594 to GSM MSC in accordance with the GSM A-interface protocol. Toallocate resources for processing the call in accordance with the typeof service indicated in assignment request 582 and BSS service response592, BSC A-interface 206 also transmits resource allocation message 584to data processing and service options system 210. Additionally, BSCA-interface 206 allocates a connection within switch 212 (FIG. 3) tocreate a traffic channel between GSM MSC 106 and data processing andservice options system 210 to carry the traffic data associated with thecall. (Message to switch 212 not shown)

Upon receipt of assignment complete message 594, GSM MSC 106 transmitsalerting message 596 to BSC A-interface 206 in accordance with the GSMA-interface protocol, which responds by transparently forwarding themessage to selection subsystem 204 via transport message 598 whichcontains the alerting message. Selection subsystem 204 then continuesthe transparent transport by transmitting transport message 600containing the alerting message to subscriber unit 100 via the forwardlink traffic channel. The alerting message indicates that subscriberunit 100 should start to generate the ring back tone. If the call isanswered, GSM MSC 106 transmits connect message 602 to BSC A-interface206 in accordance with the A-interface protocol, and BSC A-interface 206responds by transmitting transport message 604 containing the connectmessage to selection subsystem 204. Selection subsystem 204 thencontinues to transparently forward the connect message to subscriberunit 100 by transmitting transport message 606 via the forward linktraffic channel. Upon receipt of transport message 606, subscriber unit100 ceases generation of the ring back tone, and transmits transportmessage 610 containing a connect acknowledge to selection subsystem 204.Selection subsystem 204 responds by transparently forwarding the connectacknowledge to BSC A-interface 206 via transport message 612, which thentransmits connect acknowledge message 614 to GSM MSC 106 in accordancewith the GSM A-interface protocol. Upon receipt of connect acknowledgemessage 614 by GSM MSC 106, a steady state call has been established.

FIG. 8 is a message sequence diagram illustrating the signaling messagesexchanged during subscriber unit originated call release performed inaccordance with one embodiment of the invention. A subscriber unitinitiated call release is the disconnection of a telephone call inresponse to a release request by subscriber unit 100 of FIG. 2. Thesubscriber unit originated call release begins during an ongoingtelephone call or other communication by tearing down the networkconnection when subscriber unit 100 transmits transport message 652containing a disconnect message to selection subsystem 204 via thereverse link traffic channel. Selection subsystem 204 responds byforwarding the disconnect message via transport message 657 to BSCA-interface 206 causing BSC A-interface 206 to transmit disconnectmessage 672 to GSM MSC 106 in accordance with the A-interface protocol.GSM MSC 106 initiates the release of the network connection to the otherparty and transmits release message 673 to BSC A-interface 206. Inresponse, BSC A-interface 206 transmits transport message 665 containingthe release to selection subsystem 204. Selection subsystem 204 thenforwards the release via transmission of transport message 658 tosubscriber unit 100 via the forward link traffic channel.

Subscriber unit 100 responds by transmitting transport message 653containing a release complete to selection subsystem 204 via the reverselink traffic channel. Selection subsystem 204 forwards the releasecomplete via transmission of transport message 660 to BSC A-interface206. BSC A-interface responds by forwarding release complete message 676to GSM MSC 106 in accordance with the GSM A-interface protocol. GSM MSC106 responds with clear command 674 to BSC A-interface 206, inaccordance with the GSM A-interface protocol, which indicates thebi-directional radio link should be released as well as all A-interfacenetwork resources.

Upon receipt of clear command 674, BSC A-interface 206 generates a setof messages for causing traffic channel interface teardown. The trafficchannel interface teardown begins when BSC A-interface 206 transmits BSSservice disconnect message 668 to selection subsystem 204. Additionally,BSC A-interface 206 instructs switch 212 to eliminate the trafficchannel connection between data processing and service options system210 and GSM MSC 106. (Message not shown) Selection subsystem 204acknowledges the receipt of BSS service disconnect request message 668by transmitting BSS service disconnect response 670 which causes BSCA-interface 206 to transmit BSS radio link release request 663 toselection subsystem 204. Upon receipt of BSS radio link release request663 , selection subsystem 204 transmits release order 651 to subscriberunit 100 via the forward link traffic channel. Subscriber unit 100responds by transmitting release order 650 to selection subsystem 204via the reverse link traffic channel. Selection subsystem 204 thentransmits end forward traffic channel command 654 and disconnect request655 to BTS 102. BTS 102 releases the resources used to process theforward and reverse link traffic channels and then transmits end reverselink traffic channel 656 and disconnect response 659 to selectionsubsystem 204.

Selection subsystem 204 then transmits release resource request 662 toBTS 102, and BTS 102 responds by transmitting release resource response661 to selection via the reverse link traffic channel. Upon receipt ofrelease resource response, selection subsystem 204 transmits radiorelease response 664 to BSC A-interface 206 which responds bytransmitting call release request 666 to selection subsystem 204.Selection subsystem 204 then transmits call release response to BSCA-interface 206 and releases the selection resources associated with thetelephone call. BSC A-interface 206 then transmits deallocate request671 to call control processor 202 indicating that the selection andservice resources associated with the telephone call have been released,and are available for processing other calls. BSC A-interface 206 alsoindicates that the call has been released to GSM MSC 106 by transmittingclear complete 675 in accordance with the GSM A-interface protocol.Clear complete 675 indicates to GSM MSC 106 that the call processingresources are now available. Call control processor 202 responds todeallocate request 671 by transmitting deallocate response 667 to BSCA-interface 206. Upon receipt of deallocate response 667 by BSCA-interface 206, the call has been released.

FIG. 9 is a message sequence diagram illustrating the signaling messagesexchanged during network initiated call release performed in accordancewith one embodiment of the invention. A network initiated call releaseis the disconnection of a telephone call in response to a requestoriginating at a system other than a subscriber unit 100 of FIG. 2. Thenetwork initiated call release begins during an ongoing telephone callor other communication. GSM MSC 106 initiates the network teardown bytransmitting disconnect message 772 to BSC A-interface 206 in accordancewith the GSM A-interface protocol. BSC A-interface 206 responds byforwarding transport message 757 containing the disconnect to selectionsubsystem 204 which forwards transport message 753 also containing thedisconnect to subscriber unit 100 via the forward link traffic channel.Subscriber unit 100 then transmits transport message 758 containing arelease message to selection subsystem 204 which forwards transportmessage 765 containing the release message to BSC A-interface 206 inresponse. BSC A-interface 206 then transmits release message 773 to GSMMSC 106 in accordance with the GSM A-interface protocol. GSM MSC 106responds by transmitting release complete message 776 to BSC A-interface206 in accordance with the GSM A-interface protocol. BSC A-interface 206forwards transport message 760 containing a release complete toselection subsystem 204 which responds by forwarding transport message752 also containing the release complete to subscriber unit 100 via theforward link traffic channel.

GSM MSC 106 requests the release of the bi-directional radio link withthe transmission of clear command 774 to BSC A-interface 206 inaccordance with the GSM A-interface protocol. Upon receipt of clearcommand 774, BSC A-interface 206 begins traffic channel interfaceteardown substantially in accordance with the IS95 call model. Thetraffic channel interface teardown begins when BSC A-interface 206transmits BSS service disconnect message request 768 to selectionsubsystem 204. Additionally, BSC A-interface 206 instructs switch 212 torelease the traffic channel connection between data processing andservice options system 210 and GSM MSC 106. (Message not shown)Selection subsystem 204 acknowledges the receipt of BSS servicedisconnect request message 768 by transmitting BSS service disconnectresponse 770, which causes BSC A-interface 206 to transmit BSS radiolink release request 763 to selection subsystem 204. Upon receipt of BSSradio link release request 763, selection subsystem 204 transmitsrelease order 751 to subscriber unit 100 via the forward link trafficchannel. Subscriber unit 100 responds by transmitting release order 750to selection subsystem 204 via the reverse link traffic channel.Selection subsystem 204 then transmits end forward traffic channelcommand 754 and disconnect request 755 to BTS 102. BTS 102 releases theresources used to process the forward and reverse link traffic channelsand then transmits end reverse link traffic channel 756 and disconnectresponse 759 to selection subsystem 204.

Selection subsystem 204 then transmits release resource request 762 toBTS 102, and BTS 102 responds by transmitting release resource response761 to selection via the reverse link traffic channel. Upon receipt ofrelease resource response, selection subsystem 204 transmits BSS radiolink release response 764 to BSC A-interface 206 which responds bytransmitting BSS call release request 766 to selection subsystem 204.Selection subsystem 204 then transmits BSS call release response 769 toBSC A-interface 206, and releases the selection resources associatedwith the telephone call being released. BSC A-interface 206 thentransmits BSS deallocate request 771 to call control processor 202indicating that the selection and service resources associated with thetelephone call have been released and are available for processing othercalls. BSC A-interface 206 also indicates that the call has beenreleased to GSM MSC 106 by transmitting clear complete 775 in accordancewith the GSM A-interface protocol. BSC A-interface responds to BSSdeallocate request 771 by transmitting BSS deallocate response 767 toBSC A-interface 206. Upon receipt of BSS deallocate response 767 by BSCA-interface 206, the call has been released.

FIGS. 10A and 10B show a message sequence diagram illustrating thesignaling messages exchanged during a subscriber unit registrationperformed in accordance with one embodiment of the invention. During asubscriber unit registration, a subscriber unit 100 of FIG. 2 notifiesGSM MSC 106 of its present location and status so that GSM MSC 106 mayprovide service to that subscriber unit 100. The subscriber unitregistration begins with channel request message 806 transmitted fromsubscriber unit 100 to BTS 102 via the reverse link access channel. Inthe preferred embodiment of the invention, channel request message 806indicates that subscriber 100 is initiating a registration, however,this information may be provided in other messages in alternativeembodiments of the invention. BTS 102 responds to channel request 806 bytransmitting BSS channel request 810 to BSC A-interface 206 and BTSacknowledge message 808 to subscriber unit 100, although thetransmission of BTS acknowledge message 808 is optional in the preferredembodiment of the invention. BSC A-interface 206 responds by generatinga set of messages to establish a bi-directional CDMA modulated RF signalinterface between subscriber unit 100 and BTS 102 by transmitting BSScall setup request 812 to call control processor 202. Call controlprocess 202 allocates a selector and service for the call and indicatesthe result to BSC A-interface 206 in BSS call setup response 814. Uponreceiving BSS call setup response 814, BSC A-interface 206 transmitsselector call setup request 816 to selection subsystem 204. Selectorsubsystem 204 responds by allocating a selection resource for processingthe telephone call, and by indicating such to BSC A-interface 206 withselector call setup response 818. Upon receipt of call setup response818, BSC A-interface 206 transmits radio link setup request 819 toselection subsystem 204. Selection subsystem 204 responds bytransmitting channel resource request 820 to BTS 102.

Upon receipt of channel resource request 820, BTS 102 allocates channelprocessing resources to modulate and demodulates the forward and reverselink traffic channels associated with the telephone call and transmitschannel resource response message 822 to selection subsystem 204.Selection subsystem 204 responds by transmitting connect request 824 toBTS 102 which responds by transmitting connect response 826 to selectionsubsystem 204. Selection subsystem 204 then transmits null traffic data828, begin traffic data message 830, and null traffic data 832 to BTS102. BTS 102 responds to begin traffic data message 830 and null trafficdata 832 by transmitting null traffic data 836 to subscriber unit 100via the forward link traffic channel. Selection subsystem 204 alsotransmits radio link resource message 834 to BSC A-interface 206. Uponreceipt of radio link resource message 834, BSC A-interface 206transmits BTS channel assignment message 838 to BTS 102 which respondsby transmitting channel assignment message 840 to subscriber unit 100via the forward link paging channel. Subscriber unit 100 uses theassigned channel information contained in channel assignment message 840to being processing the data received via the assigned forward linktraffic channel, and it transmits reverse link traffic channel preamble842 so that BTS 102 can acquire the reverse link traffic channel. Oncethe reverse link signal has been acquired, BTS 102 transmits beginreverse link message 844 to selection subsystem 204. Selection subsystem204 responds by transmitting reverse link acknowledge 846 to subscriberunit 100 via the forward link traffic channel. As noted above, messagessuch as reverse link acknowledge 846 exchanged between selectionsubsystem 204 and subscriber unit 100 pass through BTS 102, but areshown as routed directly for ease of drawing. Additionally, selectionsubsystem 204 transmits radio link setup response 848 to BSC A-interface206. At this point, a bi-directional channel is established.

Subscriber unit 100 initiates the registration procedure by transmittingDTAP location update request 850 to selection subsystem 204. Selectionsubsystem 204 routes the location update request to BSC A-interface 206which initiates an SCCP connection with GSM MSC 106 as specified in theGSM A interface protocol. After storing the classmark information, BSCA-interface 206 generates an SCCP connection request message containingcomplete layer three information message 852 which contains BSS locationrequest 851. Complete layer three information message 852 is part of theGSM A-interface protocol and therefore well known in the art. GSM MSC106 responds by transmitting authentication request 853 to BSCA-interface 206 which in turn forwards transport message 854 containingthe authentication request to selection subsystem 204. Selectionsubsystem then forwards transport message 855 containing theauthentication request to subscriber unit 100 via the forward linktraffic channel. Subscriber unit 100 passes the transportedauthentication request to its GSM based message processing portion whichresponds to authentication request 855 by transmitting transportauthentication response 856 to selector subsystem 204 via the reverselink traffic channel. Selection subsystem 204 transparently forwards theauthentication response by transmitting transport message 857 to BSCA-interface 206. BSC A-interface 206 then transmits authenticationresponse 858 to GSM MSC 106 in accordance with the GSM A-interfaceprotocol. GSM MSC 106 responds by transmitting cipher mode command 859to BSC A-interface 206. BSC A-interface 206 then begins encryptioninitiation procedures by transmitting BSS cipher mode command 860 toselection subsystem 204 which transmits cipher mode command 862 tosubscriber unit 100 via the forward link traffic channel. Afterprocessing cipher mode command 862, subscriber unit 100 transmits ciphermode complete message 864 in encrypted form via the reverse link trafficchannel to selection subsystem 204. Upon receiving BSS cipher modecommand 860, selection subsystem 204 begins to performencryption-decryption on all additional signaling and call dataassociated with the telephone call. Selection subsystem 204 thentransmits BSS cipher mode complete message 866 to BSC A-interface 206.BSC A-interface 206 responds by transmitting cipher mode completecommand 868 to GSM MSC 106 in accordance with the GSM A-interfaceprotocol.

GSM MSC 106 then transmits ID request 874 to BSC A-interface 206 inaccordance with the GSM A-interface protocol, and BSC A-interface 206responds by forwarding the ID request via transport message 872 toselection subsystem 204. Selection subsystem 204 then transmitstransport message 870 containing the ID request to subscriber unit 100via the forward link traffic channel. The GSM based message processingportion of subscriber unit 100 responds by generating an ID response andsubscriber unit 100 transmits that ID response within transport message880 to selection subsystem 204 via the reverse link traffic channel.Selection subsystem 204 then forwards the ID response via transmissionof transport message 878 to BSC A-interface 206 which responds byforwarding ID response 876 to GSM MSC 106 in accordance with the GSMA-interface protocol. GSM MSC 106 receives ID response 876 and transmitslocation update accepted 882 to BSC A-interface 206 in accordance withthe GSM A-interface protocol. BSC A-interface 206 then transmitstransport message 886 containing location update accepted to selectionsubsystem 204, which responds by forwarding location update accepted tosubscriber unit 100 by transmitting transport message 890 via theforward link traffic channel. Subscriber unit 100 responds bytransmitting transport message 891 containing a temporary mobilesubscriber identity (TMSI) reallocation command to selection subsystem204, and selection subsystem 204 then transmits transport message 892containing transport TMSI reallocation command to BSC A-interface 206.BSC A-interface 206 responds by transmitting TMSI reallocation command894 to GSM MSC 106 in accordance with the GSM A-interface protocol. Uponreceipt of TMSI reallocation command 894, GSM MSC 106 transmits clearcommand 896 to BSC A-interface 206 to initiate the release of the radiolink.

Referring now to FIG. 10B, which continues to illustrate the signalingmessages exchanged during a subscriber unit registration performed inaccordance with one embodiment of the invention, BSC A-interface 206transmits BSS radio link release request 902 to selection subsystem 204after receiving clear command 896. Upon receipt of BSS radio linkrelease request 902, selection subsystem 204 transmits release order 900to subscriber unit 100 via the forward link traffic channel. Subscriberunit 100 responds by transmitting release order 904 to selectionsubsystem 204 via the reverse link traffic channel. Selection subsystem204 then transmits end forward traffic channel command 906 anddisconnect request 908 to BTS 102. BTS 102 releases the resources usedto process the forward and reverse link traffic channels and thentransmits end reverse link traffic channel indication 908 and disconnectresponse 910 to selection subsystem 204. Selection subsystem 204transmits release resource request 914 to BTS 102, and BTS 102 respondsby transmitting release resource response 916. Upon receipt of releaseresource response 916, selection subsystem 204 transmits BSS radiorelease response 918 to BSC A-interface 206, which responds bytransmitting BSS call release request 920 to selection subsystem 204.Selection subsystem 204 then transmits BSS call release response 922 toBSC A-interface 206, and releases the selection resources associatedwith the telephone call. BSC A-interface 206 transmits BSS deallocaterequest 924 to call control processor 202 indicating that the selectionand service resources associated with the telephone call have beenreleased and are available for processing other calls. In addition, BSCA-interface 206 indicates the call has been released to GSM MSC 106 bytransmitting clear complete 926 in accordance with the GSM A-interfaceprotocol. Call control processor 202 responds to BSS deallocate request924 by transmitting BSS deallocate response 928 to BSC A-interface 206.When deallocate response 928 is received by BSC A-interface 206, thelocation update procedure is complete.

By performing call initiation and subscriber unit registration by firstestablishing a CDMA over-the-air interface between the subscriber unit100 and BSS 105, and then by establishing a network telecommunicationsnetwork connection between subscriber unit 100 and GSM MSC 106 via thetransmission of signaling messages via those forward and reverse linktraffic channels, the use of a wireless telecommunications systemutilizing a CDMA over-the-air interface in conjunction with the GSMA-interface protocol is made possible. The ability to provide CDMA overthe interface in conjunction with the GSM A-interface network is alsomade possible via the use of a BSC A-interface that receives GSMA-interface messages, and that examines those GSM A-interface messagesand takes various actions in response. These actions include convertingthe GSM A-interface signaling messaging into an internal BSS protocol,and determining the proper response to each message based on theconfiguration and capabilities of the CDMA over-the-air interface. Theproper responses include allocating signal processing resources inresponse to an assignment request. The ability to provide CDMA over theinterface in conjunction with the GSM A-interface network is alsofacilitated by the use of a selector element that detects whenencryption messages are transmitted and that subsequently begins theencryption process. This allows the encryption feature of the GSMA-interface network to be provided along with the soft handoff featureof the IS-95 over-the-air protocol.

FIG. 11 is a block diagram of BSC A-interface 206 when configured inaccordance with one embodiment of the invention. Message processing andgeneration system 990, SS7 stack interface 992 and BSC packet interface994 are coupled together via local bus 996. During operation, SS7 stackinterface 992 passes signaling messages transmitted in accordance withthe GSM A interface with GSM MSC 106. SS7 stack interface 992 alsopasses the data associated with the signaling messages to messageprocessing and generation system 990. Additionally, message processingand generation system 990 exchanges signaling messages with BSC packetinterface 994 via local bus 996. BSC packet interface 994 responds byplacing the signaling message data received into BSS network packets,and by extracting signaling message data from BSS network packets andproviding that data to message processing and generation system 990.Message processing and generation system 990 performs the variousmessage determination and signaling message generation functions of BSCA-interface 206 as described above in response to the signaling messagedata received. Message processing and generation system 990, SS7interface stack 992, and BSC packet interface 994 are each comprised ofa semiconductor based microprocessor and a memory storage system in thepreferred embodiment of the invention, although a single microprocessorand memory system with sufficient processing power could be used toimplement any two or all three of these systems in alternativeembodiments of the invention.

FIG. 12 is a block diagram of a subscriber unit 100 when configured inaccordance with one embodiment of the invention. Forward link RF signalstransmitted from a BTS 102 (FIG. 3) are received by antenna 980 andpassed to RF processing system 982. RF processing system 982downconverts the signals to baseband and digitizes the baseband signals.Digital signal processing system 984 processes the digitized basebandsignals in accordance with the CDMA protocol used to process the signalsat transmission. As noted above, the CDMA protocol used in the preferredembodiment of the invention is that associated with the physical signalmodulation techniques of the IS-95 protocol, although the use of otherCDMA protocols is consistent with the operation of the presentinvention. The signal processing performed by digital signal processingsystem 984 includes demodulation with the forward link spreading codeand channel code, as well as Viterbi decoding and block deinterleaving,the use of which is well known in the art. This processing is performedon a frame by frame basis. The resulting frames of digital data fromdigital signal processing system 984 are passed to control system 986.Control system 986 receives the frames of digital data and determines ifthe digital data is a signaling message or user data based on headerinformation contained in each frame. User data is passed to input outputsystem 988 which normally converts the user data into audio information,but which can also provide the user data in digital format for furtherprocessing by other digital systems. Signaling data is assembled intosignaling messages which are further categorized by control system 986into transport signaling messages or local signaling messages viaexamination of messages header bits.

A non-transport or local signaling message is passed to interfacecontrol 987 which processes the message and generates any appropriateresponse. The appropriate response includes the configuration of digitalsignal processing system 986 for the reception and transmission ofbaseband digital signals by providing the necessary spreading andchannel codes, as well as the generation of outgoing signaling messagesthat are transmitted to BTS 102 of FIG. 4 via a non-transport frame inaccordance with the various call processing procedures described above.Transport signaling messages are passed to network control 989, which isreferred to as the GSM message processing portion of the subscriber unit100. Network control 989 processes the local signaling message andgenerates an appropriate response which can include the generation ofoutgoing signaling messages in accordance with the various callprocessing procedures described above. Outgoing signaling messagesgenerated by network control 989 are placed into transport messages bycontrol system 986, and are forwarded along with outgoing signalingmessages from interface control 987 to digital signal processing system984 which Viterbi encodes, block interleaves, modulates and spreads thedata in accordance with CDMA signal processing techniques. The CDMAprocessed data is passed to RF signal processing system 982 whichgenerates a quadrature phase shift key (QPSK) reverse link RF signalusing the digital data in accordance with the IS95 standard which istransmitted to a BTS 102 of FIG. 4.

In the preferred embodiment of the invention digital signal processingsystem 984 is comprised of a digital signal processor (DSP) controlledby software stored in memory system (Not shown). Additionally, controlsystem 986 is comprised of a microprocessor also controlled by softwareinstructions stored in a memory system (Not shown). Portions of thesoftware instructions used to control the microprocessor are used toimplement interface control 987 and network control 989. In alternativeembodiments of the invention, control system 986 and digital signalprocessing system 984 may be implemented via the use of one or morecustom designed integrated circuits where network control 989 andinterface control are a portion of the integrated circuits used toimplement control system 986. Furthermore, while in the configurationshown, control system 986 is coupled between input output system 988 anddigital signal processing system 984. In alternative embodiments of theinvention each of those three systems may be coupled together via theuse of mutually shared data bus. Additionally, control system 986 anddigital signal processing system 984 may share the use of the samememory system via the shared data bus, or by placement on the sameintegrated circuit.

Thus a method and apparatus for providing wireless telecommunicationservice using a CDMA over the interface and a GSM communications networkis described. The previous description of the preferred embodiments isprovided to enable any person skilled in the art to make or use thepresent invention. The various modifications to these embodiments willbe readily apparent to those skilled in the art, and the genericprinciples defined herein may be applied to other embodiments withoutthe use of the inventive faculty. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

We claim:
 1. A base station controller, including: a) a CDMA RFinterface module configured to provide a bi-directional interface with asubscriber unit; b) a GSM A-interface transport module configured toprovide a bi-directional interface with GSM MSC; c) a transparentsignaling transport module, coupled to the CDMA RF interface module andto the GSM A-interface transport module; d) signal processing resources;and d) a processing and service conversion module, coupled to the signalprocessing resources, the CDMA RF interface module, the GSM A-interfacetransport module, and to the transparent signaling transport module, theprocessing and service conversion module being configured to receive andexamine signaling messages from the CDMA RF interface module and the GSMA-interface and to configure and control the signal processing resourcesin response to such signaling messages.
 2. The base station controllerof claim 1, wherein the signaling messages received from the GSMA-interface transport module are received by the GSMA-interfacetransport as messages defined in the GSM A-interface protocol and thesignaling messages received from the CDMA RF interface module arereceived by the CDMA RF interface as messages defined in the CDMA airinterface protocol.
 3. The base station controller of claim 1, whereinthe configuration and control of the processing resources includesallocation of vocoding resources in accordance with the requested typeof service.
 4. The base station controller of claim 1, wherein theconfiguration and control of the processing resources includesallocation of devocoding resources in accordance with the requested typeof service.
 5. The base station controller of claim 1, wherein theconfiguration and control of the processing resources includesinvocation of CDMA based encryption capabilities.
 6. The base stationcontroller of claim 5, wherein the encryption capabilities are CDMAbased.
 7. The base station controller of claim 1, wherein theconfiguration and control of the processing resources includesallocation of CDMA traffic channel processing resources at the start ofthe signaling exchange between a subscriber unit and the base stationcontroller.
 8. The base station controller of claim 1, wherein theconfiguration and control of the processing resources includesallocation of CDMA traffic channel selection resources at the start ofthe signaling exchange between a subscriber unit and the base stationcontroller.
 9. The base station controller of claim 1, wherein thetransparent signaling transport module is configured to allow messagesreceived by the GSM A-interface transport module to be transmitted bythe CDMA RF interface module without intermediate examination,modification, or use.
 10. The base station controller of claim 9,wherein at least some of the messages received by the GSM A-interfacetransport module are direct transfer application messages defined in GSMspecifications.